1. Field of the Invention
The present invention relates to fluid-actuated devices for displacing a member from one position to another. More particularly the invention concerns actuators suitable to transfer a linear input motion to a rotary output motion for controlling of operation of valves provided with rotating member, e.g. butterfly valves, ball valves etc.
It should be appreciated, however, that the invention could be employed for actuating of other valves, which require for controlling of their operation rotating of a member by approximately 90 degrees between an open and closed position.
2. Description of the Related Art
There are known various rotary actuators used for actuating of rotary valves. Typically the rotary actuators employ pressurized fluid Entering an expandable chamber to drive a piston, which is mechanically connected to the valve stem and closes or opens it.
There are known in the art also so-called helical rotary actuators, in which upon applying of hydraulic or pneumatic pressure to one side of a piston the linear stroke of the piston rod is converted to rotational movement of a driving member that is engaged with a valve. This conversion is achieved by virtue of the fact that the driving member is provided with rollers, which engage helical slots formed in the wall of the piston. The piston is provided with a means for preventing twisting, when the rollers slide within the helical slots. Accordingly the piston is allowed to linearly reciprocate, while twisting motion is transferred to the driving member. An example of such helical rotary actuator is described in EP50466, EP622574, in U.S. Pat. No. 3319925, in GB1193190 etc.
The problem, which should be dealt with this type of rotary actuators, is associated with the fact that special measures should be provided to reliably prevent twisting of the piston due to the torque concentrated at the ends of the housing surrounding the driving member and the piston.
One known solution to this problem can be found in U.S. Pat. No. 2998805, in which for preventing twisting of the piston a key is formed in an outer wall of the piston, which engages a slot formed in the inner wall of a surrounding internal chamber of the housing of the piston. Another solution based on this principle can be found in U.S. Pat. No. 3,184,214.
There exists also a solution of this problem by virtue of fixing rods, which are mounted on the base plate of the actuator at one side thereof The rods extend longitudinally within the piston and form a fixed stop, which prevents the piston from twisting but at the same time does not obstruct axial displacement of the piston during the stroke, since the piston can slide over the rods.
This solution is implemented for example in a rotary actuator disclosed in DE19756425. This actuator produces twisting force, which is opposed by the fixing rods.
It is known, however, that during operating of butterfly valves and ball valves, the maximum of torque is required in the very beginning of opening and in the end of closing action. Accordingly the twisting force associated with the torque reaches its maximum, when it is applied to the most distant point of the rods. In other words the bending moment acting on the fixing rods reaches its maximum when the actuator begins its operation. Accordingly the bending moment is proportional to the length of the rods. This requires design of robust and strong rods, which renders actuator unjustified cumbersome and heavy. Therefore the achievable load, which could be developed by such actuators, is not exploited fully, since it is dictated by the actuator size, which in its turn limits the rods strength. For example, in practice an actuator with piston diameter of 100 mm provides torque not more than about 50-75 Nm.
Due to this limitation the majority of commercially available actuators are employed for operating of valves, which do not require applying of high torques. Although this might satisfy such applications like control the flow of milk, vine, juice, oil or other food products, nevertheless this is not sufficient for heavy-duty applications, e.g. petrochemical applications, oil industry, chemical plants etc.
There is known still further solution, which has been devised to overcome the above-mentioned limitation. This solution is employed for example in helical valve actuators manufactured by company SGRM, France or by company Kiesselman, Germany. According to this solution the actuator is provided with two fixing rods, which go through the piston body and extend along the whole length of the actuator chamber. The opposite ends of the rods are screwed in corresponding through openings provided at opposite sides of the chamber. Since the rods go through the piston appropriate sealing ring is provided between each rod and the piston to prevent leakage of the pressurized fluid media and at the same time to allow the piston to slide over the rods without twisting.
The advantage of this design is associated with the fact, that much higher torques can be safely developed by the actuator and applied to a valve. On the other hand, reciprocating sliding of the piston is associated with intensive wear of the scaling rings and therefore leakages may often occur during operation of the actuator, which significantly shorten its service life.
In conclusion it should be emphasized that despite numerous helical actuators for operating of rotary valves have been devised there is a need for a new and improved actuator, which is simple, inexpensive, convenient in manufacturing and exploitation and which ensures efficient and reliable operation.
The object of the present invention is to provide a new and improved helical rotary valve actuator enabling sufficiently reduce or overcome the above-mentioned drawbacks of the known in the art solutions.
The main object of the present invention is to provide a new and improved actuator, which combines advantages of the known in the art actuators, but is free of their drawbacks.
In particular one of the objects of the invention is to provide such helical actuator, which is capable to develop high torque irrespective of the length of fixing rods and piston diameter.
Still further object of the invention is to devise such helical actuator, in which there is no leakage is possible between the fixing rods and piston and which accordingly has increased service life.
Yet another object of the invention is to devise such helical actuator, which has very simple construction and which can be inexpensively and easily fabricated.
The further object of the present invention is to provide new and versatile helical actuator, which is suitable for controlling operation of valves in a wide range of industrial applications irrespective of type and flow rate of liquid, passing through the valve.
The above and other objects and advantages of the present invention can be achieved in the actuator, which main embodiment is defined as follows.
An actuator for operating a valve provided with rotatable valve member, said actuator comprising:
a tubular housing, having a longitudinal axis, said housing is defined by a peripheral cylindrical wall and by two opposite end walls, said housing is in fluid communication with a source of pressurized fluid medium, said housing accommodating therein
a piston, mounted with possibility for reciprocating linear stroke motion along the longitudinal axis in a forward and a backward direction between one end wall and the opposite end wall, said piston is defined by a concentric with the housing periphery body portion arid by a first end and by a second end, said piston is actuatable from at least one end thereof,
an operating rod, which is operatively coupled with the piston with possibility for rotation about the longitudinal axis upon reciprocating stroke motion of the piston, said operating rod is adapted to output a rotation moment to the valve member,
a cam follower arrangement for transferring the piston reciprocating stroke motion into rotation of the operating rod, said arrangement comprises at least one cam follower means, which is associated with the operating rod and is displaceable along a helical path provided in the piston,
at least two fixing rods, which are rigidly secured at one end wall of the cylinder vis-à-vis the first end of the piston, said fixing rods extend parallel to the longitudinal axis and enter into respective blind passages provided at the second piston end to enable linear stroke motion,
wherein said actuator is provided with at least two additional fixing rods, which are rigidly secured at the opposite end wall of the cylinder vis-à-vis the second piston end, said additional fixing rods extend parallel to the longitudinal axis and enter into respective blind passages provided at the second piston end to enable linear stroke motion.
The present invention has only been summarized briefly. For better understanding of the present invention as well of its advantages, reference will now be made to the following description of its various embodiments with reference to the accompanying drawings.